The construction of a deflection yoke and its placement on a CRT are subject to critical specifications and tolerances in order to meet the operating requirements and performance standards of the resultant video apparatus, such as a television receiver or a computer monitor. The placement and alignment of the deflection yoke on the CRT of the video apparatus is determined by adjusting the position of the yoke to optimize several performance parameters, including color purity and convergence. Once the desired yoke position is attained, the yoke must be attached to the CRT in a manner that maintains the position of the yoke after the yoke holding and adjusting fixture is removed.
A typical yoke-to-CRT attachment arrangement includes a clamp near the rear of the yoke to fix its longitudinal position on the CRT neck. The front of the yoke is then adjusted, by tilting, to optimize, for example, electron beam convergence at the edges of the CRT display screen. The front of the yoke is then fixed relative to the CRT, preferably by an adhesive. Such an arrangement is described in T. B. Lyden U.S. Pat. No. 4,616,265, issued Oct. 7, 1986. The patented yoke attachment arrangement described therein utilizes two adhesives having different hardening rates. Each adhesive comprises a multi-component adhesive system. Adhesives identified as epoxies, polyurethanes, polyesters, or acrylics have been used. The first adhesive temporarily holds the yoke to the tube and the second adhesive, having a hardening rate slower than the first adhesive, combines with the first adhesive to permanently bond the yoke to the tube. It has been determined that the adhesives utilized in the above-referenced patent may place undesirable stresses on the CRT glass due to differences in the thermal expansion properties of the glass and the adhesive. Additionally, the types of adhesives identified in the patent are rigid when cured and transmit any mechanical shock directly to the glass of the CRT. Removal of the deflection yoke also may be difficult if replacement or repair of the deflection yoke is required, because the rigid adhesives aggressively bond to the glass and cause the glass to spall during yoke removal. The use of flexible adhesives such as silicone adhesives has been impractical, because of the very slow cure rate of such materials.
B. E. Lock et al. U.S. Pat. No. 4,786,973, issued on Nov. 22, 1988 to overcomes the problem of direct attachment of the yoke to the CRT by introducing a flexible mounting sleeve between the yoke and the CRT. The sleeve is removably attached to the tube and closely conforms to the tube contour. The yoke is then adhesively mounted in the sleeve to permit removal or replacement of the deflection yoke without causing damage to the tube. A drawback of the flexible sleeve is that the sleeve and its attachment to the tube increase both the material and manufacturing costs of the yoke-tube combination.
Thus, a need exists for an adhesive composition for direct attachment of the yoke to the tube that will cure quickly, remain sufficiently flexible upon curing to prevent damage to the glass envelope of the tube, and permit removal or replacement of the deflection yoke.